1. Field of the Invention
Generally, the present disclosure relates to the manufacture of sophisticated semiconductor devices, and, more specifically, to various methods of forming stressed channel regions on 3D semiconductor devices, such as, for example, FinFET semiconductor devices, through use of epitaxially formed materials to thereby form channel regions having enhanced mobility characteristics.
2. Description of the Related Art
The fabrication of advanced integrated circuits, such as CPU's, storage devices, ASIC's (application specific integrated circuits) and the like, requires the formation of a large number of circuit elements in a given chip area according to a specified circuit layout, wherein so-called metal oxide field effect transistors (MOSFETs or FETs) represent one important type of circuit element that substantially determines performance of the integrated circuits. A FET is a planar device that typically includes a source region, a drain region, a channel region that is positioned between the source region and the drain region, and a gate electrode positioned above the channel region. Current flow through the FET is controlled by controlling the voltage applied to the gate electrode. If there is no voltage applied to the gate electrode, then there is no current flow through the device (ignoring undesirable leakage currents, which are relatively small). However, when an appropriate voltage is applied to the gate electrode, the channel region becomes conductive, and electrical current is permitted to flow between the source region and the drain region through the conductive channel region.
To improve the operating speed of FETs, and to increase the density of FETs on an integrated circuit device, device designers have greatly reduced the physical size of FETs over the years. More specifically, the channel length of FETs has been significantly decreased which has resulted in improving the switching speed of FETs. However, decreasing the channel length of a FET also decreases the distance between the source region and the drain region. In some cases, this decrease in the separation between the source and the drain makes it difficult to efficiently inhibit the electrical potential of the source region and the channel from being adversely affected by the electrical potential of the drain. This is sometimes referred to as a so-called short channel effect, wherein the characteristic of the FET as an active switch is degraded.
In contrast to a FET, which has a planar structure, there are so-called 3D devices, such as an illustrative FinFET device, which is a 3-dimensional structure. More specifically, in a FinFET, a generally vertically positioned fin-shaped active area is formed and a gate electrode encloses both sides and an upper surface of the fin-shaped active area to form a tri-gate structure so as to use a channel having a 3-dimensional structure instead of a planar structure. In some cases, an insulating cap layer, e.g., silicon nitride, is positioned at the top of the fin and the FinFET device only has a dual-gate structure. Unlike a planar FET, in a FinFET device, a channel is formed perpendicular to a surface of the semiconducting substrate so as to reduce the physical size of the semiconductor device. Also, in a FinFET, the junction capacitance at the drain region of the device is greatly reduced, which tends to reduce at least some short channel effects.
Device designers have recently employed channel stress engineering techniques on FETs to improve the electrical performance of such devices, i.e., to improve the mobility of the charge carriers. More specifically, such stress engineering techniques generally involve creating a tensile stress in the channel region for an NMOS transistor and creating a compressive stress in the channel region for a PMOS transistor. Stress engineering techniques typically involve the formation of specifically made silicon nitride layers that are selectively formed above appropriate transistors, i.e., a layer of silicon nitride that is intended to impart a tensile stress in the channel region of an NMOS transistor would only be formed above the NMOS transistors. Conversely, for PMOS transistors, a layer of silicon nitride that is intended to impart a compressive stress in the channel region of a PMOS transistor is formed above the PMOS transistors. The techniques employed in forming such nitride layers with the desired tensile or compressive stress are well known to those skilled in the art. Other techniques employed to induce the desired stress on a FET involves forming recesses or cavities in the substrate where source/drain regions will be formed and thereafter forming a stress-inducing material, such as an epitaxially formed silicon/germanium material, in the cavities to induce the desired stress in the channel region of the transistor.
In general, stress engineering techniques for FinFETs have generally involved forming stress-inducing layers of material over or within the source and drain regions of the FinFET. As noted above, a FinFET is a 3-dimensional device where stress engineering techniques may be very complex to implement. Therefore, there is a need for various methods and structures to improve carrier mobility in FinFETs.
The present disclosure is directed to various methods of forming stressed channel regions on 3D semiconductor devices, such as, for example, FinFET semiconductor devices, through use of epitaxially formed materials to thereby enhance the performance characteristics of such 3D devices by forming channel regions having enhanced mobility characteristics.